The above-referenced U.S. patent application Ser. Nos. 09/120,598, 09/165,435, and 09/328,514 (the xe2x80x9cPreceding Applicationsxe2x80x9d), form the background of the present invention. In these Preceding Applications, the inventors disclosed their inventions as generally relating to at least partial removal of occlusive material from a body lumen or vessel with acoustic phenomena resulting from radiation energy pulses delivered through optical fiber media to the vessel. The inventors disclosed their inventions as relating more particularly to methods and apparatus for generating fluid flow within a body vessel to facilitate disruption of occlusive material and recanalization of the occluded vessel. The inventors used the term xe2x80x9cclotxe2x80x9d to refer to a thrombus, embolus or some other partial or total occlusion of a vessel, and the term xe2x80x9cemulsifyxe2x80x9d, or the term xe2x80x9cchewxe2x80x9d, to mean to disrupt occlusive material by photoacoustic or mechanical or other phenomena to generate particle(s) smaller than the original occlusive material. These terms also apply to the present invention.
In the Preceding Applications, the inventors disclosed techniques and apparatus that use pulsed radiation energy to generate fluid flow and/or to perform mechanical work within a body lumen or vessel. These techniques and apparatus were disclosed as being useful to recanalize a body vessel by disrupting a partial or total occlusion therein. These techniques and apparatus were disclosed as having application in the removal of such an occlusion or obstruction from a vessel within the human body, and more particularly, a partial or total clot from a cerebral blood vessel, where that clot has caused ischemia or an ischemic stroke. These techniques and apparatus were disclosed as being particularly useful for timely removal of such a clot to avoid causing collateral damage to the vessel.
The above-referenced Preceding Applications, the inventors disclosed methods and apparatus for attracting occlusive material within a vessel to a photoacoustic source of disruption, so as to potentially enhance the amount and/or degree of disruption obtained. The apparatus was disclosed as being flexible at its distal tip to facilitate access to occlusive material that may be located in a remote, tortuous vessel pathway.
The foregoing and other principles of the Preceding Applications have application in the present invention.
The present invention generally provides an apparatus having at least one inlet port, at least one outlet port, and at least one optical fiber having a distal end positioned relative to the ports such that when pulsed radiation energy is delivered to a body vessel via the optical fiber, fluid is caused to pass through the inlet port and to travel towards the outlet port, preferably past the optical fiber distal end. The repetitive formation and collapse of bubbles in the ambient fluid creates this flow phenomenon, which in turn results from the repetitive absorption of radiation pulses by the fluid. This flow phenomenon can be used to enhance the total or partial mechanical disruption or emulsification of occlusions with photoacoustic phenomena (as described in the above-mentioned Ser. No. 08/955,858 application) by causing ambient fluid and occlusive material to be drawn towards the recanalization apparatus. The invention can also result in localized emulsification of occlusive material or partial or complete removal of that material from the body. The capability of radiation energy to cause mechanical work to be performed is demonstrated by the present invention.
Multiple fibers can be arranged in such a manner that one or more fibers generate the pumping phenomenon and/or one or more fibers contribute to the clot emulsification by generating the acoustic phenomena described in the Ser. No. 08/955,858 application, and/or one or more fibers contribute to mechanical disruption of the clot as disclosed herein, for example. Multiple outlet ports are arranged in various tubing materials in such a way as to maintain a flexible distal tip portion of the apparatus while also maintaining column strength of the distal portion.
The use of very small diameter optical fibers allows the desired pumping to be achieved and acoustic waves to be generated with a relatively low amount of radiation pulse energy, thereby keeping the amount of heat input to the vessel at a low level. Proper thermal management according to the present invention reduces the likelihood of damaging the walls of the blood vessel adjacent the occlusion, which is especially important for the relatively thin walled vessels of the brain in which the invention has application. Accordingly, radiation pulses not causing the desired fluid flow or not being efficiently converted into the desired acoustic waves may be terminated in order to prevent providing energy that heats the region without doing useful work, as has been described in the above-mentioned related applications.
The present invention encompasses methods and flexible apparatus for delivering radiation energy to a radiation-absorbing fluid within the apparatus to generate a series of expanding and collapsing bubbles therein, and thereby generate flow in a fluid surrounding the apparatus. Effective fluid flow is obtained via at least one optical fiber, disposed within the apparatus near a distal opening therein, that, when fired, tends to pump fluid with respect to the apparatus, and at least one other optical fiber, disposed within the apparatus in the vicinity of a side opening thereof, that, when fired, tends to agitate fluid near its distal end.
Preferably, the apparatus includes one xe2x80x9cpumpxe2x80x9d fiber and multiple xe2x80x9cchewxe2x80x9d or emulsification fibers, such as four chew fibers. The pump fiber is preferably secured within a distal section of the apparatus at a point proximal to the distal opening. The chew fibers are preferably arranged within an intermediate section of the apparatus, proximal to the distal section. Preferably, this intermediate section has a number of openings that corresponds to the number of chew fibers. In this embodiment, each of the chew fibers is arranged such that its distal end is located in a vicinity of a corresponding opening and can act upon fluid located near or passing through that opening.
The pumping and chewing actions of the fibers within the device cause a net fluid motion that is particularly effective in disrupting a partial or total occlusion in a body passage, such as a blood vessel, within which the apparatus is operated. While a relatively low level of radiation energy or power may be used for such applications, such as the energy or power level disclosed in the Preceding Applications, it may be desirable to increase the energy or the power to obtain greater disruption effects. The present apparatus is adapted to provide a cooling medium to the body passage to avoid causing any substantial thermal injury to the walls of the passage, particularly when the apparatus is operated over a broader range of power parameters. By way of example, the apparatus may be operated using an applied power level of from about 0.5 to about 2 W to obtain an average power level at the distal end of the apparatus of from about 0.5 to about 2 W, or of from about 0.5 to about 1.5 W using a duty cycle, as may be desirable or necessary. The apparatus may be operated at the higher levels within these ranges particularly when active cooling is provided.
Active cooling encompasses the provision of a cooling medium through a lumen of the apparatus to its intermediate and/or distal sections, from which the medium may travel within the apparatus and/or out of the openings therein into the body vessel. The cooling medium is a radiation-absorbing fluid, such as blood or a dye-based coolant, such as a coolant containing blue dye. A suitable coolant may be chosen based on a variety of factors, such as the selected radiation and the radiation-absorption characteristics of the coolant for that radiation, or the viscosity characteristics of the coolant, for example, a viscosity conducive to appropriate fluid mechanics upon operation of the apparatus. The flow rate of the coolant may be varied according to various operational parameters, but will generally be from about 0.5 to about 3 cc/minute.
The present invention allows one to operate the apparatus over broader ranges of energy and power than formerly believed safe or practicable. These ranges include energy and power levels that are more effective in emulsification processes. By way of example, in the disruption of porcine clot, ex vivo, better results have been achieved when using a blood analog coolant and operating the inventive apparatus at an average power of about 1 W, than when using a previous apparatus with the same coolant at the same average power. Further by way of example, in the disruption of porcine clot, ex vivo, even better results have been achieved when using either a red-dye coolant or a blue-dye coolant in place of the blood-analog coolant and operating the inventive apparatus at an average power of about 1 W.
Additional objects, features and advantages of the various aspects of the present invention will be better understood from the following description of its preferred embodiments, which description should be taken in conjunction with the accompanying drawings.